Astronomical ToolsAstronomical Tools

Guiding QuestionsGuiding Questions

1.1. What methods do scientists use to expand our What methods do scientists use to expand our understanding of the universe?understanding of the universe?

2.2. What makes up our solar system?What makes up our solar system?3.3. How does measuring angles help astronomers How does measuring angles help astronomers

learn about objects in the sky?learn about objects in the sky?4.4. What is powers-of-ten notation, and why is it What is powers-of-ten notation, and why is it

useful in astronomy?useful in astronomy?5.5. Why do astronomers measure distances in Why do astronomers measure distances in

astronomical units, light-years, and parsecs?astronomical units, light-years, and parsecs?6.6. How does studying the cosmos help us on How does studying the cosmos help us on

Earth?Earth?

Scientific MethodsScientific Methods Scientific MethodScientific Method

– based on observation, logic, and skepticismbased on observation, logic, and skepticism HypothesisHypothesis

– a collection of ideas that seems to explain a a collection of ideas that seems to explain a phenomenonphenomenon

ModelModel– hypotheses that have withstood observational or hypotheses that have withstood observational or

experimental testsexperimental tests TheoryTheory

– a body of related hypotheses can be pieced together a body of related hypotheses can be pieced together into a self consistent description of natureinto a self consistent description of nature

Laws of PhysicsLaws of Physics– theories that accurately describe the workings of theories that accurately describe the workings of

physical reality, have stood the test of time and been physical reality, have stood the test of time and been shown to have great and general validityshown to have great and general validity

Uncover the FUncover the Formation of ormation of SSolar olar SSystemystem

– The star we call the Sun and all the celestial bodies that The star we call the Sun and all the celestial bodies that orbit the Sunorbit the Sun including Earthincluding Earth the other eight planetsthe other eight planets all their various moonsall their various moons smaller bodies such as asteroids and cometssmaller bodies such as asteroids and comets

AAngngular Measureular Measure Astronomers use Astronomers use angular measureangular measure to to

– describe the apparent size of a celestial objecdescribe the apparent size of a celestial objectt degree (degree (°)°): t: the basic unit of angular measure he basic unit of angular measure

– One entire cycle is 360One entire cycle is 360°° AAngular diameterngular diameter, , or or angular sizeangular size

– ThThe Moon is ½° or the Moon e Moon is ½° or the Moon subtends subtends an angle of ½°.an angle of ½°.

AAngular distancengular distance:: If you draw lines from your eye to each If you draw lines from your eye to each of two stars, the angle between these lines is the of two stars, the angle between these lines is the angular angular distancedistance..

AAngngular Measureular Measure

The adult human hand held at arm’s length provides a The adult human hand held at arm’s length provides a means of estimating anglesmeans of estimating angles

– About 10About 10°° for the fist for the fist– About 1About 1°° for the finger for the finger

AAngngular Measureular Measure

Angular MeasurementsAngular Measurements Subdivide one degree into 60 Subdivide one degree into 60 arcminutesarcminutes

– minutes of arcminutes of arc– abbreviated as 60 arcmin or 60´abbreviated as 60 arcmin or 60´

Subdivide one arcminute into 60 Subdivide one arcminute into 60 arcsecondsarcseconds– seconds of arcseconds of arc– abbreviated as 60 arcsec or 60”abbreviated as 60 arcsec or 60”

1° = 60 arcmin = 60´1° = 60 arcmin = 60´

1´ = 60 arcsec = 60”1´ = 60 arcsec = 60”

For exampleFor example– Moon: 1800 arcsecMoon: 1800 arcsec– Saturn: 20 arcsecSaturn: 20 arcsec– A star: much less than 1 arcsec, can not be resolved by A star: much less than 1 arcsec, can not be resolved by

any telescopeany telescope

Powers-of-ten notationPowers-of-ten notation

Notation:CNotation:Common Prefixesommon Prefixes

Factor Name Symbol

(billion) 109 Giga- G (1,000,000,000)

(million) 106 Mega- M (1,000.000)

(thousand) 103 kilo- K (1,000)

(hundredth) 10-2 centi- c (0.01)

(thousandth) 10-3 milli- m (0.001)

(millionth) 10-6 micro- (0.000001)

(billionth) 10-9 nano- n (0.000000001)

Powers-of-ten notationPowers-of-ten notation

149,600,000 km, the average distance between the Sun 149,600,000 km, the average distance between the Sun and the Earthand the Earth149.6 million km149.6 million km1.496 X 101.496 X 1088 km in scientific notation km in scientific notation

Units of Units of Astronomical Astronomical DDistancesistances Astronomical Unit (AU)Astronomical Unit (AU)

– One AU is the average distance between Earth and the SunOne AU is the average distance between Earth and the Sun– 1.496 X 101.496 X 1088 km or 92.96 million miles km or 92.96 million miles– Jupiter: 5.2 AU from the SunJupiter: 5.2 AU from the Sun

Light Year (ly)Light Year (ly)– One ly is the distance light can travel in one year at a speed of about One ly is the distance light can travel in one year at a speed of about

3 x 103 x 1055 km/s or 186,000 miles/s km/s or 186,000 miles/s– 9.46 X 109.46 X 101212 km or 63,240 AU km or 63,240 AU– Proxima Centauri, the nearest star: 4.2 lyProxima Centauri, the nearest star: 4.2 ly

Parsec (pc)Parsec (pc)– the distance at which 1 AU subtends an angle of 1 arcsecthe distance at which 1 AU subtends an angle of 1 arcsec– 1 pc = 3.09 × 101 pc = 3.09 × 101313 km = 3.26 ly km = 3.26 ly– Milky Way galaxy: 50 kpcMilky Way galaxy: 50 kpc

Units of Units of Astronomical Astronomical DDistancesistances